Kawaii is Japanese for "cute". Many japanese culture/entertainment fans have taken the word and added it to their lingo to be used in english conversation.
It can be used in several sentence patterns, including a question such as "Kawaii ne?" meaning "Cute, isn't it?"
"Kawaii!!!!" (Upon seeing a picture of an underage japanese schoolgirl)
"Kawaii ne?" (A cosplayer showing off his/her costume to others, or vainly looking in the mirror)
SirGuy: "I have to hang with my kawaii bro, so I'll be seein you later!"